Hydraulic fluid circuits, also called hydraulic systems, are commonly used in automatic transmissions and transfer cases. These systems are typically used to actuate a coupling, with the coupling usually made up of a piston and a clutch pack. The system also typically includes an actuator for delivering fluid to the coupling to build fluid pressure behind the piston to apply the clutch pack.
One problem that can occur when using a hydraulic circuit in any type of application is that air can get into the system and affect the hydraulic system performance. Specifically, air in the system can have an effect of how the actuator will build fluid pressure in the coupling. Occasionally, the system needs to “bleed off,” this is a process by which the air is purged from the system, so normal operation can be resumed. Prior methods of allowing the system to bleed off include the use of a manually operated bleed valve. The manually operated bleed valve is part of a closed loop hydraulic system that can be used to purge air from the system prior to operation. The use of a manual bleed valve has several disadvantages, one of which is the fact that the valve is manually operated, instead of being automatically operated. Also, manual bleed valves do not always release all of the air in the system.
Accordingly, there exists a need for an improved controllable bleed valve in a hydraulic circuit.